Heat 1 tablespoon oil in a large nonstick pan over medium high heat.
Add ground beef and break it up into smaller chunks.
Cook until browned and no longer pink. It does not have to be fully cooked.
Drain fat and transfer this beef to slow cooker.
In the same pan, add remaining 1 tablespoon oil and heat over medium high heat.
Add onion, celery, carrots, garlic, potatoes and sute for 2-3 minutes until garlic is fragrant. The potatoes don't need to be fully cooked.
Transfer veggie mixture to the crockpot.
Add broth, beef bouillon base, Worcestershire sauce, thyme, rosemary, bay leaf, salt, pepper, tomato paste and mix until combined.
Cover and cook on Low heat for for 6-7 hours or until veggies (especially potatoes) are tender but not mushy.
Mix in cornstarch slurry and let it cook uncovered for 5-10 minutes on Low heat until stew is thickened slightly.
If you prefer a thinner stew, mix in some more broth. If you prefer a thicker stew, continue cooking uncovered for longer or mix in a bit more cornstarch slurry.
Discard sprigs of thyme and rosemary as well as the bay leaf.
Garnish with fresh parsley and enjoy.